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Control of cortex development by ULK4, a rare risk gene for mental disorders including schizophrenia

View Article: PubMed Central - PubMed

ABSTRACT

Schizophrenia is a debilitating familial neuropsychiatric disorder which affects 1% of people worldwide. Although the heritability for schizophrenia approaches 80% only a small proportion of the overall genetic risk has been accounted for, and to date only a limited number of genetic loci have been definitively implicated. We have identified recently through genetic and in vitro functional studies, a novel serine/threonine kinase gene, unc-51-like kinase 4 (ULK4), as a rare risk factor for major mental disorders including schizophrenia. Now using the approach of in utero gene transfer we have discovered that Ulk4 plays a key modulatory role in corticogenesis. Knockdown of Ulk4 leads to significantly decreased cell proliferation in germinal zones and profound deficits in radial migration and neurite ramification. These abnormalities can be reversed successfully by Ulk4 gene supplementation. Ulk4 also regulated acetylation of α-tubulin, an important post-translational modification of microtubules. We conclude that Ulk4 plays an essential role in normal brain development and when defective, the risk of neurodevelopmental disorders such as schizophrenia is increased.

No MeSH data available.


Related in: MedlinePlus

Silencing Ulk4 massively perturbs radial migration and neurite arborization.(A) In the control cortex, almost all the neurons traced with GFP at E15.5 have migrated successfully into layers II–III at P7; (B) Instead of being present in superficial layers, large amounts of GFP-traced cells are “trapped” in cortical layers IV–VI in shRNA268 knockdown groups. (C,D,F) Ulk4 knockdown with shRNA268 dramatically reshapes neurite branching. Most of the mislocated GFP neurons bear a stalled apical dendrite (white arrows) with some having an ectopic apical dendrite (C, asterisks and yellow arrow; F, asterisks) or long secondary dendritic branching (F, white arrowheads). (E) In the control brains, GFP-positive pyramidal neurons develop a predominant apical dendrite (white arrows) which ends and elaborates in layer I. White broken line shows the pial surface and the yellow broken line delineates the boundary between lamina I and II. (G) Compared with control brains (black columns), there are significantly more cells in deeper cortical lamina and subtantially less cells in layers II–III in the shRNA268 knockdown cortex (gray columns). *p < 0.05. **p < 0.01. (H,I) Compared with control brains (H), shRNA269 leads to dispersed layers II–III which contain loosely-packed GFP cells (I). White arrow in I shows a neuron with two apical dendrites which is also enlarged in inset i. (J–N) Confocal images of abnormal cell morphology in shRNA269 knockdown brains. Some cells develop multiple dendrites directly from the soma with (N, white arrow, and inset n) or without the predominent apical dendrite (J, white arrow). Inset n is the enlarged view of the white arrowed neuron in N. In addition, many GFP-positive cells have stalled (K,L, white arrows) or aborted (K,L, slim white arrows) apical dendrites which are frequently replaced by ectopic apical dendrites (K,L, white arrowheads) or long secondary dendritic branching (K, asterisks). (M) Clusters of GFP-postive cells are disoriented and do not present typical polarity of pyramidal neurons (aligned perpendicularly to brain surface). Broken white lines in (J,N) indicate the brain surface and the boundary between layers I and II in (M). Bars = 100 μm in (A,B), 20 μm in (C–N) and associated insets.
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f4: Silencing Ulk4 massively perturbs radial migration and neurite arborization.(A) In the control cortex, almost all the neurons traced with GFP at E15.5 have migrated successfully into layers II–III at P7; (B) Instead of being present in superficial layers, large amounts of GFP-traced cells are “trapped” in cortical layers IV–VI in shRNA268 knockdown groups. (C,D,F) Ulk4 knockdown with shRNA268 dramatically reshapes neurite branching. Most of the mislocated GFP neurons bear a stalled apical dendrite (white arrows) with some having an ectopic apical dendrite (C, asterisks and yellow arrow; F, asterisks) or long secondary dendritic branching (F, white arrowheads). (E) In the control brains, GFP-positive pyramidal neurons develop a predominant apical dendrite (white arrows) which ends and elaborates in layer I. White broken line shows the pial surface and the yellow broken line delineates the boundary between lamina I and II. (G) Compared with control brains (black columns), there are significantly more cells in deeper cortical lamina and subtantially less cells in layers II–III in the shRNA268 knockdown cortex (gray columns). *p < 0.05. **p < 0.01. (H,I) Compared with control brains (H), shRNA269 leads to dispersed layers II–III which contain loosely-packed GFP cells (I). White arrow in I shows a neuron with two apical dendrites which is also enlarged in inset i. (J–N) Confocal images of abnormal cell morphology in shRNA269 knockdown brains. Some cells develop multiple dendrites directly from the soma with (N, white arrow, and inset n) or without the predominent apical dendrite (J, white arrow). Inset n is the enlarged view of the white arrowed neuron in N. In addition, many GFP-positive cells have stalled (K,L, white arrows) or aborted (K,L, slim white arrows) apical dendrites which are frequently replaced by ectopic apical dendrites (K,L, white arrowheads) or long secondary dendritic branching (K, asterisks). (M) Clusters of GFP-postive cells are disoriented and do not present typical polarity of pyramidal neurons (aligned perpendicularly to brain surface). Broken white lines in (J,N) indicate the brain surface and the boundary between layers I and II in (M). Bars = 100 μm in (A,B), 20 μm in (C–N) and associated insets.

Mentions: The strong expression of Ulk4 transcripts in the post-mitotic neurons prompted us to investigate the influence of Ulk4 on radial migration, a precisely-controlled process by which neurons move from their site of origin to the final laminar position. To address this question, we examined the distribution of GFP-traced cells in the P7 brains which underwent electroporation at E15.5. In the control group, the majority of neurons (born on E15.5) have completed migration and settled compactly in layers II–III (Fig. 4A), a highly vulnerable target region in schizophrenia. Strikingly, in the shRNA268 knockdown brains, GFP-positive neurons were located in loose arrays within layers II–III. In addition, many neurons were scattered along the migration route, and many others appeared trapped in the deeper cortical lamina close to the corpus callosum (Fig. 4B). We counted the number of GFP-positive cells in each individual layer and performed statistical comparison. The results show that compared with control brains (n = 3), knockdown brains contained significantly less GFP-positive cells in layers II–III (n = 3, p < 0.001), but high proportions of these cells in deeper layers (IV–VI) (p < 0.001) (Fig. 4G), indicating a dramatically delayed neuronal migration.


Control of cortex development by ULK4, a rare risk gene for mental disorders including schizophrenia
Silencing Ulk4 massively perturbs radial migration and neurite arborization.(A) In the control cortex, almost all the neurons traced with GFP at E15.5 have migrated successfully into layers II–III at P7; (B) Instead of being present in superficial layers, large amounts of GFP-traced cells are “trapped” in cortical layers IV–VI in shRNA268 knockdown groups. (C,D,F) Ulk4 knockdown with shRNA268 dramatically reshapes neurite branching. Most of the mislocated GFP neurons bear a stalled apical dendrite (white arrows) with some having an ectopic apical dendrite (C, asterisks and yellow arrow; F, asterisks) or long secondary dendritic branching (F, white arrowheads). (E) In the control brains, GFP-positive pyramidal neurons develop a predominant apical dendrite (white arrows) which ends and elaborates in layer I. White broken line shows the pial surface and the yellow broken line delineates the boundary between lamina I and II. (G) Compared with control brains (black columns), there are significantly more cells in deeper cortical lamina and subtantially less cells in layers II–III in the shRNA268 knockdown cortex (gray columns). *p < 0.05. **p < 0.01. (H,I) Compared with control brains (H), shRNA269 leads to dispersed layers II–III which contain loosely-packed GFP cells (I). White arrow in I shows a neuron with two apical dendrites which is also enlarged in inset i. (J–N) Confocal images of abnormal cell morphology in shRNA269 knockdown brains. Some cells develop multiple dendrites directly from the soma with (N, white arrow, and inset n) or without the predominent apical dendrite (J, white arrow). Inset n is the enlarged view of the white arrowed neuron in N. In addition, many GFP-positive cells have stalled (K,L, white arrows) or aborted (K,L, slim white arrows) apical dendrites which are frequently replaced by ectopic apical dendrites (K,L, white arrowheads) or long secondary dendritic branching (K, asterisks). (M) Clusters of GFP-postive cells are disoriented and do not present typical polarity of pyramidal neurons (aligned perpendicularly to brain surface). Broken white lines in (J,N) indicate the brain surface and the boundary between layers I and II in (M). Bars = 100 μm in (A,B), 20 μm in (C–N) and associated insets.
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f4: Silencing Ulk4 massively perturbs radial migration and neurite arborization.(A) In the control cortex, almost all the neurons traced with GFP at E15.5 have migrated successfully into layers II–III at P7; (B) Instead of being present in superficial layers, large amounts of GFP-traced cells are “trapped” in cortical layers IV–VI in shRNA268 knockdown groups. (C,D,F) Ulk4 knockdown with shRNA268 dramatically reshapes neurite branching. Most of the mislocated GFP neurons bear a stalled apical dendrite (white arrows) with some having an ectopic apical dendrite (C, asterisks and yellow arrow; F, asterisks) or long secondary dendritic branching (F, white arrowheads). (E) In the control brains, GFP-positive pyramidal neurons develop a predominant apical dendrite (white arrows) which ends and elaborates in layer I. White broken line shows the pial surface and the yellow broken line delineates the boundary between lamina I and II. (G) Compared with control brains (black columns), there are significantly more cells in deeper cortical lamina and subtantially less cells in layers II–III in the shRNA268 knockdown cortex (gray columns). *p < 0.05. **p < 0.01. (H,I) Compared with control brains (H), shRNA269 leads to dispersed layers II–III which contain loosely-packed GFP cells (I). White arrow in I shows a neuron with two apical dendrites which is also enlarged in inset i. (J–N) Confocal images of abnormal cell morphology in shRNA269 knockdown brains. Some cells develop multiple dendrites directly from the soma with (N, white arrow, and inset n) or without the predominent apical dendrite (J, white arrow). Inset n is the enlarged view of the white arrowed neuron in N. In addition, many GFP-positive cells have stalled (K,L, white arrows) or aborted (K,L, slim white arrows) apical dendrites which are frequently replaced by ectopic apical dendrites (K,L, white arrowheads) or long secondary dendritic branching (K, asterisks). (M) Clusters of GFP-postive cells are disoriented and do not present typical polarity of pyramidal neurons (aligned perpendicularly to brain surface). Broken white lines in (J,N) indicate the brain surface and the boundary between layers I and II in (M). Bars = 100 μm in (A,B), 20 μm in (C–N) and associated insets.
Mentions: The strong expression of Ulk4 transcripts in the post-mitotic neurons prompted us to investigate the influence of Ulk4 on radial migration, a precisely-controlled process by which neurons move from their site of origin to the final laminar position. To address this question, we examined the distribution of GFP-traced cells in the P7 brains which underwent electroporation at E15.5. In the control group, the majority of neurons (born on E15.5) have completed migration and settled compactly in layers II–III (Fig. 4A), a highly vulnerable target region in schizophrenia. Strikingly, in the shRNA268 knockdown brains, GFP-positive neurons were located in loose arrays within layers II–III. In addition, many neurons were scattered along the migration route, and many others appeared trapped in the deeper cortical lamina close to the corpus callosum (Fig. 4B). We counted the number of GFP-positive cells in each individual layer and performed statistical comparison. The results show that compared with control brains (n = 3), knockdown brains contained significantly less GFP-positive cells in layers II–III (n = 3, p < 0.001), but high proportions of these cells in deeper layers (IV–VI) (p < 0.001) (Fig. 4G), indicating a dramatically delayed neuronal migration.

View Article: PubMed Central - PubMed

ABSTRACT

Schizophrenia is a debilitating familial neuropsychiatric disorder which affects 1% of people worldwide. Although the heritability for schizophrenia approaches 80% only a small proportion of the overall genetic risk has been accounted for, and to date only a limited number of genetic loci have been definitively implicated. We have identified recently through genetic and in vitro functional studies, a novel serine/threonine kinase gene, unc-51-like kinase 4 (ULK4), as a rare risk factor for major mental disorders including schizophrenia. Now using the approach of in utero gene transfer we have discovered that Ulk4 plays a key modulatory role in corticogenesis. Knockdown of Ulk4 leads to significantly decreased cell proliferation in germinal zones and profound deficits in radial migration and neurite ramification. These abnormalities can be reversed successfully by Ulk4 gene supplementation. Ulk4 also regulated acetylation of &alpha;-tubulin, an important post-translational modification of microtubules. We conclude that Ulk4 plays an essential role in normal brain development and when defective, the risk of neurodevelopmental disorders such as schizophrenia is increased.

No MeSH data available.


Related in: MedlinePlus